This invention relates to an electric circuit breaker that comprises electromagnetic means for opposing the contact-repulsion forces developed when a high current flows through the circuit breaker.
When high current flows through the engaged contacts of a typical circuit breaker, high magnetic forces are developed that tend to force the contacts apart. As explained in more detail in U.S. Pat. No. 3,225,160-Barkan, assigned to the assignee of the present invention, these forces result primarily from the tendency of the current path to restrict at the point of contact engagement and, thus, to develop loop-shape components, each comprising arms extending along confronting faces of the contacts. Current through these loop shaped components creates a repulsive, contact-separating force between the arms of each loop. These contact-separating forces, which are referred to hereinafter as "contact-popping" forces, vary directly with the square of the current and, hence, can be very high when currents of short-circuit magnitude pass through the engaged contacts.
For opposing these contact-popping forces developed when high currents pass through the engaged contacts, various electromagnetic arrangements have been devised which act on the contacts to hold them engaged with a force also varying directly with the square of the current through the contacts. Typically, these electromagnetic arrangements have been rather complex and costly. For example, they have often required an electric circuit path of an involved configuration or have required that the opposing forces be transmitted through conductive braids or that there be special linkages and latches present. A problem usually present, and one which accounts for much of the above complexity, is in preventing the magnetic-assist means from unduly interfering with a circuit-breaker opening operation, which must usually be a high speed operation.